Currently, in a networking manner of a baseband unit (BBU) and a radio remote unit (RRU), one BBU can support multiple RRUs, and the BBU can be communicatively connected to each RRU by using multiple channels (also referred to as RRU channels). In actual application, to better improve quality of communication between a BBU and an RRU, a frequency response difference between RRU channels is often obtained. However, it is found in practice that, RRU channels may be interconnected by using a bridge (also referred to as an association processing network) due to some technology requirements. Therefore, an output signal of interconnected RRU channels is a mixed signal. Consequently, it is difficult to accurately obtain a frequency response difference between the interconnected RRU channels.